Rajendra N. Solanki1, Poornima S. Digge2, Rajesh Y. Viswakarma3, Kalpesh B. Patel4, Hiren N. Patel5, Harshad R. Shah6
We presented role of MDCT and high-field MRI in cochlear dimension before the cochlear implantation. In our institute, we used combo modality as HRCT and high-field MRI rather to use single modality for complete workup and for the selection of proper size electrode array.
The aim of the study is to correlate the cochlear dimensions using CT/MRI with- (1) Intraoperative surgical findings/difficulties. (2) Preoperative electrode array option selection.
MATERIALS AND METHODS
MDCT and 1.5 Tesla MRI machine was used to scan the patients. Patients screened and operated at B.J. Medical College and Civil Hospital, Ahmedabad, Gujarat. 30 patients were taken within period of 2 years from March 2009 to April 2011. All the patients underwent CT and MRI study. Cochlear implant (MED-EL, Austria) was used for this study. Each scan was obtained on a 16-section spiral CT (GE, bright speed). The studies were performed with the following parameters- 0.75-mm collimation, 0.625-mm section thickness, 140 kVp, 120 mAs, pitch of 0.8, a 15-cm field of view and a 512 x 512 matrix. The initial data sets were then reconstructed at 0.1 mm intervals.
All 15 patients also underwent MRI (GE Signa HDx 1.5T series) examination for internal auditory canal in whom FIESTA sequence was taken with flip angle 65 degrees, slice thickness 0.8 mm, matrix 256 x 320.
Thirty cases were taken for the study. Twenty patients were completely suitable for standard electrode. Six patients needed the use of insertion test device before the actual insertion of active electrode. In 3 patients, split electrode was kept as backup implant, but was finally not needed. One patient had common cavity cochlea who refused surgery because of variable outcome. Three patients had high jugular bulb. Six patients had rotated cochlea. One patient had dehiscent facial nerve at 2nd genu.
Multidetector volumetric CT scanner with 3D reconstruction and higher strength MRI provide soft tissue and bony detail with very high resolution for cochlea and also helps in minimise the intraoperative difficulties and overcoming it and also help in assessing the involvement of adjacent critical structures like internal carotid artery, jugular bulb and facial nerve.